Interaction of viruses and bacteria in host-parasite relations

The impact of respiratory viral infections in patients with cystic fibrosis

Respiratory viruses have been implicated in pulmonary exacerbations of CF and in the long-term course of pulmonary dysfunction in these patients. However, the data are by no means complete and there is the clear need for more intensive evaluations of the role of viral pathogens in this population. Further controlled prospective studies assessing the impact of viral infections in large cohorts of patients with CF are still necessary. Placebo-controlled, antiviral treatment protocols also should be initiated. In clinical practice at the present time, patients with CF should be assessed for respiratory viral infections, at least at the time of hospitalizations for pulmonary deterioration. This assessment should include obtaining specimens from the respiratory tract for viral cultures and rapid respiratory viral antigen detection. Identifying a respiratory viral infection may alter clinical care. The patient can be isolated appropriately, and it may be possible to reduce the intensive use of expensive and potentially toxic parenteral antibiotics. The role of antiviral therapy in these patients must await further evaluations. The mechanisms of the short- and long-term effects of respiratory viruses in patients with CF have not been defined. However, pathophysiologic studies conducted in normal children and adults allow the development of several plausible hypotheses. The definition of mechanisms of injury in this population must be a priority, since it may influence clinical practice. If airway obstruction is the principal mechanism of viral-induced injury, therapeutic approaches designed to relieve the obstruction would be most appropriate. For example, if the obstruction resulted from induced or aggravated reactive airway disease, the current common practice of prescribing chronic bronchodilator therapy would be appropriate. This therapy might be especially suited to those experiencing frequent viral infections. In addition, the administration of bronchodilators to patients during acute exacerbations of pulmonary disease caused by viruses might be of clinical benefit. If, on the other hand, the principal mechanism of viral-induced injury is found to be through synergistic interaction with bacteria, the current practice of aggressive antimicrobial therapy would remain appropriate.

Binding of staphylococci to mucus in vivo and in vitro

The association of Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus saprophyticus with tissues of the upper respiratory tract were compared by using an in vivo ferret model. Ferrets were challenged intranasally with a 1-ml volume of radiolabeled staphylococci (3 mg [dry weight]), were allowed to clear the bacteria in vivo for 90 min, and were sacrificed. Tissues from the right nasal fossa were harvested and processed for radioassay or histology. Of the recoverable staphylococci, greater than or equal to 96% was associated with mucus gel overlaying mucosa of the turbinates. A quantitative radioassay was developed to study the binding of labeled staphylococci to immobilized crude ferret nasal mucin (FM) and bovine submaxillary gland mucin (BM). Binding showed saturation kinetics and was blocked specifically by BM but not by human Tamm-Horsfall glycoprotein nor orosomucoid. Binding to both FM and BM was significantly inhibited (P less than or equal to 0.01) when cocci were pretreated with trypsin but not when treated with beta-galactosidase or sodium metaperiodate (except for binding of S. saprophyticus to FM). These results suggest that mucin-binding receptors of the cocci may have protein components. The staphylococcus-binding receptors of both FM and BM appear to contain protein components, based on sensitivity to pretreatment with trypsin.

Detection of staphylococcal membrane receptors on virus-infected cells by direct adhesin overlay

We partially characterized the interaction between 125I-labeled surface proteins of Staphylococcus aureus, obtained by thermal extraction, and purified plasma membranes from uninfected and influenza virus A/FM/1/47-infected Madin-Darby canine kidney cells. The radioactivity profile of surface-labeled proteins, derived from anion-exchange high-pressure liquid chromatography, showed a mixture of acidic polypeptides in a peak which contained approximately 5% of the total protein injected; adsorption with purified plasma membranes reduced radioactivity by 5 to 7% and altered elution profiles. Using a direct adhesin overlay procedure, we found that these surface-labeled proteins reacted with polypeptides located on the external surface of plasma membranes which were shared by both virus-infected and uninfected cells or were unique to virus-infected cells. Our data may help explain the enhanced adherence of S. aureus to influenza virus A-infected cells in vitro.